1. Field of the Invention
This invention relates to coin validators used in various automatic service devices of vending machines, etc., and more particularly to such validators which discern the thickness and/or pattern of a coin in a non-contact manner.
2. Description of the Related Art
There is an electronic coin validator in which a pair of electrodes are disposed on the corresponding sides of a coin path to detect the difference between the capacitances on the electrodes on standby and during coin passage to thereby validate the coin.
More specifically, as shown in FIG. 5, the validator includes a pair of opposing electrodes 2 and 3 disposed so as to face the front and back of a coin 1 along a coin path, an oscillator 4 which outputs an oscillating signal of a predetermined frequency, a resonator 7 including a coil 5 and a capacitor 6 for applying its resonant output across the electrodes 2 and 3, a buffer 8 for amplifying the output signal from the resonator 7, a rectifying and smoothing circuit 9 for rectifying and smoothing the signal received via the buffer 8, an amplifier 10 for amplifying the output signal from the rectifying and smoothing circuit 9, and a thickness/pattern detector 11 for detecting the thickness and pattern of the coin 1 in accordance with a change in the rectified output signal via the amplifier 10 during the coin passage and reporting the result of the detection to a controller 12 for control of the components of the validator.
According to this arrangement, a series resonator of a resonant frequency f.sub.O =1/2.pi..sqroot. LC is constituted by the oscillator 4 of an oscillating frequency f.sub.1, coil 5 of L Henry and capacitor 6 of capacitance of C Farad, inclusive of the capacitance between the electrodes. The resonant characteristic of FIG. 6 is represented by a resonant curve shown by the solid line a on standby wherein a voltage v.sub.1 is generated across the capacitor 6.
Under such condition, when a coin passes between the electrodes 2 and 3, the capacitance across the electrodes 2 and 3 changes and the total capacitance C changes, the resonant frequency changes from f.sub.0 to f.sub.oc and the resonant characteristic changes to the curve represented by the broken line b as shown in FIG. 6. Then the voltage across the capacitor 6 is attenuated from v.sub.1 to v.sub.1c at a frequency f.sub.1, namely, the change v.sub.1 -v.sub.1c is generated. The detector 11 uses this change to discern the thickness and pattern of the coin.
If in the conventional validator the inductance of the coil 5 or the capacitance of the capacitor 6 changes, for example, due to a change in its ambient temperature or if components themselves vary from one manufacturing lot to another, the resonant frequency f.sub.0 changes, for example, like f.sub.0 ' in FIG. 6 and the characteristic curve moves to the curve shown by the dot dashed line c, and thus the output voltage v.sub.1 from the capacitor 6 on standby is attenuated to v.sub.1 '. Thus the difference between the output v.sub.1c obtained during the coin 1 passage and the voltage v.sub.1 ' is reduced to thereby lose the stability of the validation undesirably.
It is an object of the present invention to provide a coin validator which is capable of discerning the thickness or pattern of a coin in a stabilized manner.